First piloted in the Pennsylvania, New Jersey, Northern Virginia, and the Greater Washington, DC metro area regions, the program turns customers' routers into quasi-public Wi-Fi access points.

While only open to subscribers, and requiring a password-authenticated connection, Comcast subscribers can now access a portion of their neighbor's bandwidth. Comments an Xfinity spokesperson:

Comcast’s newest Wireless Gateway broadcasts two Wi-Fi signals. By default, one is securely configured for the private use of the home subscriber. The second is a neighborhood 'xfinitywifi' network signal that can be shared. This creates an extension of the Xfinity Wi-Fi network and will allow visiting Xfinity Internet subscribers to sign in and connect using their own usernames and passwords.

Customers can opt out by refusing Comcast's special "Gateway" and buying their own cable modems/routers. Alarmingly, though, Comcast reportedly will not give any special warning (say a mailed noticed) to customers with its Gateways before turning their devices into public access points.

The feel-good message of the Comcast quasi-public WiFi bid is dampened by legal liability.

While the idea of universal access to Comcast (whose network is fairly ubiquitous due to the weakly competitive American internet market) is an appealing one, customers willing to give up a chunk of their bandwidth for the greater good may want to pause until more details emerge. So far it's unclear how Comcast is implementing the separate signals, and whether traffic will be logged as a single IP address.

Imagine someone connects to your network and downloads illegal materials. Now your IP address -- and by proxy your home -- have been linked to that investigation. While you may eventually be vindicated, it may take federal agents months after ripping through your house to realize it was not you but one of possibly hundreds of "guest" Comcast users (or someone with one of their passwords) who accessed the network.